A gas turbine engine typically includes a vent that is formed by the fan Inner-Fixed Structure (IFS) also known as the core cowl and the core external surface also known as Core Outer Mold line (Core OML). Ideally, the vent would be located in a region where the static pressure is less than the ambient pressure to increase the Vent Nozzle Pressure Ratio (VNPR). Placing a vent in such a location for a geared turbo fan engine configuration is challenging because this type of engine has a low fan nozzle pressure ratio (FNPR). Due to the low fan nozzle pressure ratio there is no over expansion region on a core cowl where the static pressure is less than the ambient pressure. Due to the low VNPR, the fan stream suppresses the vent stream which adversely affects the vent flow coefficient and results in an increase in the physical vent exit area requirement.
Additionally, the geared turbo fan configuration has a smaller turbine diameter, which reduces a circumferential width of the vent. Thus, to meet the vent exit area requirement, the height of the vent step is increased. This increase in height results in an increase in vent step drag as associated with a backward facing step, which adversely affects efficiency.